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| United States Patent |
5,124,098
|
|
Vischer
|
June 23, 1992
|
Process for producing foam fiber
Abstract
There is described a process for producing polyester foam fiber where
sodium carbonate and citric acid are added as blowing agent before
spinning together with polycarbonate. The proportion of blowing agent is
from 0.15 to 0.80 percent by weight of the polyester and the proportion of
polycarbonate is from 0.5 to 2 percent by weight of the polyester. The
process of the invention makes it possible to produce foam fiber, i.e.
filament or staple fiber with discontinuous voids, which may be used for
example as carpet fiber and filling fiber for blankets and cushions or as
a lining material for winter clothing.
| Inventors:
|
Vischer; Axel (Augsburg, DE)
|
| Assignee:
|
Hoechst Aktiengesellschaft (Frankfurt am Main, DE)
|
| Appl. No.:
|
665680 |
| Filed:
|
March 7, 1990 |
| Current U.S. Class: |
264/54; 264/165; 521/79; 521/81; 521/92; 521/97; 521/138; 521/182 |
| Intern'l Class: |
B28B 011/18; C08J 009/08 |
| Field of Search: |
521/138,182,92,97,79,81
264/54,165
|
References Cited
U.S. Patent Documents
| 3884030 | May., 1975 | Baxter et al. | 428/397.
|
| 4164603 | Aug., 1979 | Siggel et al. | 428/398.
|
| 4425443 | Jan., 1984 | Georlette et al.
| |
| 4544594 | Oct., 1985 | Li et al. | 428/92.
|
| 4572740 | Feb., 1986 | Kretzschmann et al.
| |
| 4588754 | May., 1986 | Liu | 521/138.
|
| Foreign Patent Documents |
| 0059495 | Sep., 1982 | EP.
| |
| 0158212 | Oct., 1985 | EP.
| |
| 2550081 | Apr., 1977 | DE.
| |
| 2550080 | May., 1977 | DE.
| |
| 2703051 | Jul., 1978 | DE.
| |
| 103375 | Jan., 1974 | DD.
| |
| 1543423 | Apr., 1979 | GB.
| |
| 1558308 | Dec., 1979 | GB.
| |
Primary Examiner: Foelak; Morton
Claims
I claim:
1. A process for producing foam fiber from a synthetic polyester, a blowing
agent, and an additive, which process comprises:
admixing into the polyester an alkali metal bicarbonate and citric acid, as
a blowing agent, and an effective amount, sufficient to reduce degradation
of the melt viscosity of the polyester which occurs when the polyester is
in the molten state, of a polycarbonate different from the aforesaid
polyester, and
spinning the resulting mixture, with expansion, to obtain the foam fiber.
2. The process of claim 1, wherein the level of blowing agent is from 0.15
to 0.80 percent by weight of the polyester.
3. The process of claim 2, wherein the polyester is polyethylene
terephthalate and the level of blowing agent is from 0.15 to 0.4 percent
by weight of the polyester.
4. The process of claim 2, wherein the polyester is polybutylene
terephthalate and the level of blowing agent is from 0.3 to 0.6 percent by
weight of the polyester.
5. The process of claim 1, wherein the level of polycarbonate is from 1.0
to 1.5 percent by weight of the polyester.
6. The process of claim 1, wherein the effective amount of polycarbonate is
0.5 to 2% by weight, based on the weight of the polyester.
7. The process of claim 1, wherein the blowing agent is a mixture
consisting essentially of sodium bicarbonate and citric acid in the sodium
bicarbonate:citric acid weight ratio of from 1:3 to 3:1.
8. The process of claim 1, wherein the polyester is polyethylene
terephthalate or polybutylene terephthalate.
9. The process as claimed in claim 1, wherein the foam fiber is produced by
extruding and spinning said resulting mixture.
10. The process as claimed in claim 1, wherein the foam fiber is produced
by melt-spinning and drawing said resulting mixture.
11. The process as claimed in claim 1 wherein polyester, a blowing agent,
and polycarbonate are first mixed and then melted.
12. The process as claimed in claim 11, wherein polyester, blowing agent,
and polycarbonate are mixed in chip form before melting, the flowing agent
being added in the form of a masterbatch.
13. The process of claim 12, wherein the blowing agent masterbatch includes
a polyolefin.
Description
The invention relates to a process for producing foam fiber as classified
in the preamble of claim 1.
Foam fiber, i.e. fiber in filament or staple form with discontinuous voids,
is used as carpet fiber and also as filling fiber for blankets and
cushions or as a lining material for anoraks and other winter clothing. An
advantage of foam fiber is its low density and hence the relatively large
volume of filling material per unit weight. To obtain a noticeable
reduction in density, the ready-produced, crimped foam fiber should have a
void content of about 15%. Since the void content decreases on drawing,
the void content after spinning must be appropriately larger. As regards
crimping, the void spaces must be sufficiently stable to crushing. A
process for producing foam fiber from a synthetic high polymer, a blowing
agent and an additive is known from DE Auslegeschriften 2,550,080 and
2,550,081. In these prior art processes the high polymer used is a
polyester such as polyethylene terephthalate or a polyamide such as
nylon-6 or nylon-66. The blowing, i.e. gas-forming, agent used is a
low-boiling hydrocarbon such as pentane or hexane or a hydrocarbon which
is gaseous at room temperature such as propane or butane. The additive
used is a silicone oil which is said to improve the spinnability of the
polymer, increase the lifetime of the spinning die and ensure uniform
distribution of the voids.
DD Patent 103,375 discloses a process for producing foam fiber from
isotactic polypropylene wherein the blowing agent used is sodium
bicarbonate and citric acid and the additive used is again silicone oil.
Sodium bicarbonate and citric acid are also used as blowing agent in the
production of foamed plastics, for example structural foam moldings; cf.
for example EP 0 059 495 and 0 158 212. The plastics mentioned therein
also include, inter alia, various high polymers such as polyester. Even
though sodium carbonate and citric acid do give good foam formation with
polyesters, it has been found that this blowing agent damages the
polyester. For example, it has been found that the intrinsic viscosity
decreases by 0.15 units from a starting level of approximately 0.65, which
corresponds to a molecular weight degradation of more than 20%.
It is an object of the present invention to provide a process for producing
foam fiber from a synthetic high polymer, in particular polyester, a
blowing agent and an additive whereby efficient foaming is achieved
without damage to the high polymer.
This object is achieved by the process defined in claim 1.
The use of polycarbonate in the production of polyester fiber is already
known from DE Offenlegungsschrift 2,703,051. In this process, the
polyester to be spun is admixed before spinning with 3 to 20 percent by
weight of a polycarbonate in order to increase the water retention
capacity due to voids in the fiber.
In the process of the present invention, by contrast, sodium bicarbonate,
citric acid and polycarbonate are mixed into the high polymer. It has been
found, surprisingly, that the addition of polycarbonate counteracts the
degradation in the melt viscosity of the polyester which would otherwise
occur. Thus, the degradation in molecular weight of polyester from the
starting polymer to the ready-produced foam fiber has been found to be
less than 5%. The use of sodium bicarbonate and citric acid as blowing
agent has the advantage that these substances only decompose at high
temperatures and are toxicologically safe. Similarly, polycarbonate has
the advantage of toxicological safeness.
Advantageously, the blowing agent of sodium bicarbonate and citric acid is
added in an amount of from 0.15 to 0.80 percent by weight of the high
polymer and the polycarbonate is added in an amount of from 0.5 to 2
percent by weight of the high polymer.
A blowing agent of sodium bicarbonate and citric acid suitable for the
purposes of the present invention is any desired mixture of alkali metal
bicarbonate and citric acid, preferably in a weight ratio of from 1:3 to
3:1.
Preferably, the blowing agent content is from 0.15 to 0.4 percent by weight
in the case of polyethylene terephthalate and from 0.3 to 0.6 percent by
weight in the case of polybutylene terephthalate. The preferred
polycarbonate content is in both cases from 1.0 to 1.5 percent by weight.
With polybutylene terephthalate the level of blowing agent and
polycarbonate required is somewhat higher than with polyethylene
terephthalate.
The level of other substances in the polyester should be as small as
possible.
A further embodiment of the present invention provides that the high
polymer, the flowing agent and the polycarbonate be mixed in chip form -
before melting - with the blowing agent being added in the form of a
masterbatch, in particular in a polyolefin. The mixing of the three
components may take place for example in the feed line leading to the
extruder.
The process of the present invention gives foam fiber having good
processing properties (as continuous filament or staple) as carpet
material and also as filling material for clothing. Such carpet or filling
fiber material is produced by melt spinning and drawing in a conventional
manner; slight adjustment of the process parameter may be necessary on the
basis of routine experiments. When processing foam fiber in thermal
processes it is well to bear in mind that the insulating effect of the
voids also results in slower heating of the foam fiber.
EXAMPLES A
In a polyester fiber spinning plant, polyethylene terephthalate granules,
dried in a conventional manner, are mixed with sodium bicarbonate and
citric acid in the form of a blowing agent masterbatch (HOSTATRON P 1941)
and polycarbonate (MAKROLON 16063068), and the mixture is extruded and
spun through round-hole spinning dies.
__________________________________________________________________________
Spinning conditions
A1 A2 A3 A4 A5 A6
__________________________________________________________________________
Hole diameter (mm)
0.8 0.8 0.8 0.8 0.8 0.8
dtex as spun 30 30 30 30 30 30
Spinning temperature (.degree.C.)
285 285 285 285 285 285
Take-off speed (m/min)
1000 1000 1000 1000 1000 1000
Hostatron P 1941
-- 0.6 -- 0.6 0.6 1.0
(% by weight of polyester)
Polycarbonate
-- -- 1.0 1.0 2.0 1.0
(% by weight of polyester)
Result 1.34 1.31 1.34 0.97 0.92 0.92
Density of fiber
(g/cm.sup.3)
__________________________________________________________________________
The density of the fiber is a measure of the expansion of the fiber The
Examples show that only the chosen combination of blowing agent and
polycarbonate gives a significant reduction in the density, i.e a
significant void content of the fiber.
EXAMPLES B
The same starting materials are used as in Examples A, the blowing agent
HOSTATRON P 1941 being added in an amount of 0.6 percent by weight and the
polycarbonate in an amount of 1 percent by weight of the polyester. These
Examples are concerned with the investigation of spinning dies of various
hole diameters and of various spinning temperatures and take-off speeds.
__________________________________________________________________________
Spinning conditions
B1 B2 B3 B4 B5 B6
__________________________________________________________________________
Hole diameter (mm)
0.4 0.8 1.0 1.2 0.8 0.8
dtex as spun 30 30 30 30 30 21
Spinning temperature (.degree.C.)
285 285 285 285 295 285
Take-off speed (m/min)
1000 1000 1000 1000 1000 1400
Result 1.02 0.97 0.95 0.92 0.92 0.97
Density of fiber (g/cm.sup.3)
__________________________________________________________________________
EXAMPLES C
The starting materials are the same as in Examples A and B. Instead of a
spinning die with a round hole cross-section, a hollow profile spinning
die is used.
______________________________________
Spinning conditions
C1 C2
______________________________________
dtex as spun 17 17
Spinning temperature (.degree.C.)
287 287
Take-off speed (m/min)
1300 1300
Hostatron P 1941 -- 0.6
(% by weight of polyester)
Polycarbonate -- 1.0
(% by weight of polyester)
Result 1.10 0.80
Density of fiber (g/cm.sup.3)
______________________________________
EXAMPLES D
The same blowing agent and the same additive are used as in the preceding
series of examples. Instead of polyethylene terephthalate granules,
however, polybutylene terephthalate granules are used.
______________________________________
Spinning conditions
D1 D2 D3
______________________________________
Hole diameter (mm)
1.2 1.2 1.2
dtex as spun 37 37 37
Spinning temperature (.degree.C.)
267 267 267
Take-off speed (m/min)
1000 1000 1000
Hostatron P 1941
0.6 1.0 1.3
(% by weight of polyester)
Polycarbonate 0.6 1.0 1.3
(% by weight of polyester)
Result 1.26 1.15 1.04
Density of fiber (g/cm.sup.3)
______________________________________
As is evident from the table, in the case of polybutylene terephthalate
only a higher level of blowing agent and polycarbonate than required for
polyethylene terephthalate leads to a corresponding reduction in the fiber
density.
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